Manufacturer casting numbers

I know for a fact that the Ford big block is a well known casting that was used in automotive, industrial, and marine applications, but what happened to the block "AFTER" it was cast is something entirely different.

Some (actually many) of the blocks are cast as side-oilers, but only a few are actually machined as such. In addition, the machine line would also make a block ready for specified use in the irrigation fields, or for use on orchard or vinyard wind machines. Of course, marine motors have their own specific use requirements, so the 427 block has some flycut bosses (for instance, for marine motor mounts, etc) that only show up on a marine motor. Even though the castings all started the same, it is the machine line (for the Ford motors) that determined whether the motor was a full race side-oiler version, a street driven center-oiler, or a marine center-oiler. Yes, there are a few side-oilers that actually made it all the way into a marine application, and aside from the bragging rights and higher rebuild costs, they perform exactly the same as the center-oiler in the marine context.

I do not know if the small block GM versions have the same custom milling requirements, as I was sort of thinking they were all generic and could be interchanged. This is of great interest to me, so if anyone (Mark) knows of any specific differences, this would be a great topic of discussion.

Thanks!

Paul